This application claims priority to an application entitled xe2x80x9cForward Link Power Control Device and Method for Mobile Communication System Supporting Transmission Diversityxe2x80x9d filed in the Korean Industrial Property Office on Jun. 13, 1998 and assigned Ser. No. 98-22220, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a forward link power control device and method for a mobile communication system supporting transmission diversity.
2. Description of the Related Art
For power control in a mobile communication system, a receiving party measures strength of a received signal which varies according to a condition of a radio link. The receiving party then sends the result from the measurement as a power control command to a transmitting party. The transmitting party then increases or decreases power of a transmission signal according to the power control command from the receiving party.
Specifically, to control transmission power of a base station in such a mobile communication system, a mobile station measures a signal-to-interference ratio (SIR), compares it with a threshold and provides the base station with information about the comparison result through a power control bit (PCB) on a reverse channel. Upon receipt of the power control bit, the base station controls power of a transmission signal according to a value of the received power control bit. That is, for forward link power control in a mobile communication system, the mobile station measures power of a signal transmitted from the base station and provides the base station with the result from the measurement, and the base station then controls power of a transmission signal according to the power control information received from the mobile station. This is called a closed loop power control method.
With reference to FIG. 1, there is illustrated a forward link power control procedure in a mobile communication system. Referring to FIG. 1, when a base station transmits a signal 111, a mobile station receives the signal with a propagation delay 113. Upon receipt of the signal, the mobile station measures strength of the received signal and thereafter, sends a power control bit according to the measured result 115. The base station then receives the power control bit with a propagation delay 117 and controls power of a transmission signal according to a received power control bit 119. As illustrated in FIG. 1, power control is performed in a unit of power control group (PCG), and actual power control is performed with a delay of at least one power control group.
As described above, in a mobile communication station, power control is performed in a unit of power control group. The base station sends a signal, and the mobile station then measures an SIR of the signal received from the base station, compares it with a threshold and sends the base station a power control bit generated according to the comparison result. The base station then analyzes the power control bit and controls transmission power for a next power control group according to the analysis. This power control method can be applied to a case where a traffic channel is continuously transmitted via a single antenna.
However, a mobile communication system supporting the transmission diversity requires a new power control method for controlling power of a traffic channel which is switched between two or more antennas. Accordingly, a need exists for a forward link power control device and method for a mobile communication system supporting transmission diversity where transmission signals are outputted via two or more antennas.
It is, therefore, an object of the present invention to provide a device and method for controlling power of transmission signals outputted via at least two antennas in a mobile communication system supporting a transmission diversity.
It is another object of the present invention to provide a device and method for measuring power of signals transmitted via at least two antennas to generate a power control bit for controlling transmission power of a forward link in a mobile communication system having a transmission diversity function.
It is further another object of the present invention to provide a device and method for measuring power of signals output from at least two antennas, generating a power control bit by averaging the measured power, and equally controlling power of the signals being transmitted via the antennas according to the power control bit in a mobile communication system supporting the transmission diversity.
It is still further another object of the present invention to provide a device and method for separately measuring power of signals output from at least two antennas to generate power control bits, and independently controlling power of the signals being transmitted via the antennas according to the power control bits in a mobile communication system supporting the transmission diversity.
It is further another object of the present invention to provide a device and method for controlling power of transmission signals at antenna switching periods in a mobile communication system supporting a transmission diversity.
In accordance with one aspect of the present invention, there is provided a forward link power control device for a mobile communication system supporting a transmission diversity function. The power control device comprises a base station device for transmitting a traffic signal via at least two antennas, switching the traffic signal to be transmitted to any one of the two antennas based on a power control group period, and equally controlling transmission power of the traffic signal being transmitted to the antennas according to power control information received via a reverse link; and a mobile station device for receiving signals output from the antennas of the base station using one antenna, separately measuring power of a traffic signal and an interference signal received for a power control group duration which is at least twice an antenna switching time of the base station device, averaging the measured value to generate a power control information and multiplexing the power control information to a reverse link traffic signal to transmit the power control information to the base station.
In accordance with another aspect of the present invention, there is provided a transmission power control device for a base station device in a mobile communication system. The transmission power control device comprises radio frequency (RF) transmitters for transmitting a traffic signal via at least two antennas: switches for switching the traffic signal to be transmitted to any one of the two antennas based on a power control group period; and gain controllers for actually controlling transmission power of traffic signals transmitted via the antennas according to power control information received via a reverse link.
In accordance with further another aspect of the present invention, there is provided a power control device for a mobile station device in a mobile communication system including a base station device supporting a transmission diversity function. The power control device comprises an RF receiver for receiving signals output from antennas of the base station device using one antenna; an interference power measurer for measuring power of an interference signal by accumulating and averaging the interference signal received for a power control group duration which is at least twice an antenna switching time of the base station device; a traffic power measurer for measuring power of a traffic signal by accumulating and averaging the traffic signal received for a power control group duration vehicle is at least twice the antenna switching time; a power control bit generator for generating a power control bit by calculating a signal-to-interference ratio (SIR) from the traffic signal power and the interference signal power; and a multiplexer for multiplexing the power control bit to a reverse link traffic signal to transmit the power control bit to the base station device.